Treacherous Love by Beatrice Sparks

Fourteen-year-old Jennie's life is turning upside down. Her father has walked out, and her anguished mother seeks solace in pills. Her best friend practically abandons her to be with a boyfriend. It seems like Jennie's real best friend is her diary. Then she meets Mr. Johnstone, the substitute math teacher. Jennie has never met such a charismatic teacher. She feels honored when Mr. J. seems to single her out for special attention, and begins to fantasize about him as her boyfriend. When Mr. J. first reveals his feelings for her, she is thrilled by the relationship that grows outside the classroom walls. Then, slowly, Jennie's diary becomes a record of her loneliness, pain, and confusion. Will it also offer her a way to escape from this treacherous love?